A global positioning system (GPS) called satellite navigation equipment or a satellite locating system, which is a locating technology globally used, is one of the locating systems having the highest precision among locating systems which have been developed up to now.
However, in general, an error range in positioning using the GPS is 5 to 15 m and since an error of up to 30 m may be shown, performance required in general vehicle safety technology cannot be satisfied.
By considering such a point, a differential global positioning system (DGPS) is widely used in a vehicle safety technology field.
The DGPS as a GPS measurement technique of a relative positioning type complements elements that cause an error by using a reference point coordinate which has been already known and acquires more accurate positional information by maximally reducing the error.
However, since the DGPS has a limitation in that a service providing area is restricted by coverage of a base station and a position where a commercial DGPS complementation signal is serviced is too distant from the base station, positional accuracy cannot be enhanced even though the DGPS is used.
Japanese Patent Application Laid-Open No. 2008-089353 discloses a system for complementing a GPS signal of an own vehicle by receiving a DGPS signal from a road-side unit (RSU). However, this system has a problem in that traffic is significantly increased because all vehicles directly receive the DGPS signal from the road-side unit.